Servomechanism



June 4, 1968 J, R TT 3,386,303

SERVOMECHANISM Filed Oct. 20, 1965 3 Sheets-Sheet 1 INVENTOR.

JOHN CURLET T PATENT AGENT J. CURLETT SERVOMECHANISM June 4, 1968 3 Sheets-Sheet 2 Filed Oct. 20, '1965 FlG 2 FIG 3 INVENTOR.

JOHN CURLETT PATENT AGENT J CURLETT SERVOMECHAN I SM June 4, 1968 3 Sheets-Sheet 5 Filed Oct. 20, 1965 PATENT AGENT United States Patent 3,386,303 SERVOMECHANISM John Curlett, Los Gatos, Calif., assignor to Gurries Manufacturing Co., San Jose, Calif., a corporation of California Filed Oct. 20, 1965, Ser. No. 498,486 8 Claims. (Cl. 74-388) ABSTRACT OF THE DISCLOSURE A servomechanism for automatically controlling the disposition of the working implement of earth leveling equipment, such as the blade of a road grader, including a pendulum sensing unit mounted directly on the main frame of the equipment, feedback mechanism connected to the earth moving blade, and means for providing a novel control mechanism which combines the inputs from the pendulum sensing unit and the feedback mechanism to control the disposition of the blade or other earth working implement.

The present invention relates generally to servomechanisms and more particulary to servomechanisms for controlling disposition of the working implement of an earth moving or leveling machine.

A number of servomechanisms have been proposed and constructed for controlling the disposition of the working implement of earth moving and leveling machines, one example being disclosed in my prior US. Patent No. 2,971,499. However, precise control has been ditficult to achieve because of the conditions encountered in normal, every day use of such equipment. By way of example, the earth working blade of a conventional road grader encounters variable resistance (e.g., large stones) during its normal operation which introduces shock to the blade and resultant inaccuracies in the leveling operation. When it is realized that the earth leveling or grading operations for preparation of roadways frequently have specified stringent tolerances of no more than one-eighth 0/8) inch, the significance of the operational difiiculties becomes obvious.

Accordingly, it is a general object of the present invention to provide a servomechanism for automatically controlling the disposition of the working implements of earth leveling and moving equipment, such as the blade of a road grader, with an extremely high degree of accuracy.

More particularly, it is a feature of the invention to provide a servomechanism including a sensing unit which can be mounted directly on the implement or on the main frame of the equipment so as to be partially isolated from instantaneous shook encountered by the blade or other working implement which directly engages the earth.

A correlated feature of the invention is to provide a feedback mechanism between the working implement and such sensing unit which accurately indicates when the desired disposition of the working implement is attained.

For control of cross-slope disposition of the blade or other working implement, the sensing unit, in accordance with another specific feature of the invention, takes the form of a novel pendulum structure.

A related feature of the invention is the provision of a novel dampening mechanism which can be adjusted to control pendulum motion in accordance with the type of terrain being encountered by the equipment.

Specifically, it is a feature of the invention to provide a separate liquid-filled chamber for the pendulum which 3,386,303- Patented June 4, 1968 enhances the accuracy of its operation and also facilitates maintenance when required.

Additionally, it is a feature of the invention to provide a novel eccentric linkage between the sensing unit and a valve or other control member which is to be actuated thereby.

If the control member be a valve, it'is a specific feature to provide a particular form of linkage enabling use of a valve whose actuating stroke is rather short so that the valve can be highly responsive and accurate in its control function.

The control linkage is arranged in accordance with another feature of the invention to accommodate additional control inputs from a manual control or from the mentioned feedback mechanism.

More particularly, such alternate inputs incorporate mechanisms which compensate for Wear over an extended period so that accuracy of control is maintained.

In accordance with another specific feature of the invention, alternate control inputs are delivered through a novel form of reduction gearing which assures the requisite accuracy.

Additionally, it is a feature to provide such reduction gearing so that it can accommodate inputs both from the manual control and from the feedback mechanism so as to effect an overall simplification of the apparatus without detracting from its accuracy.

These as well as other objects and features of the invention will become apparent from a perusal of the following description of the exemplary embodiments of the invention shown in the accompanying drawings wherein:

FIG. 1 is a side elevational view of a servomechanism embodying the invention, portions of the housing being broken away to illustrate interior details thereof,

FIG. 2 is an end view of the FIG. 1 structure as viewed from the left thereof,

FIG. 3 is a fragmentary vertical sectional view taken along line 33 of FIG. 1 and illustrating details of a sensing unit in the form of a pendulum,

FIG. 4 is an enlarged fragmentary vertical sectional view taken along line 4-4 of FIG. 1 illustrating 'a portion of the actuating linkage for a control valve,

FIG. 5 is a horizontal sectional view taken along line 5-5 of FIG. 4,

FIG. 6 is a longitudinal vertical sectional view taken centrally through a reduction gear box appearing at the right of FIG. 1, and

FIG. 7 is a fragmentary sectional view taken along line 77 of FIG. 6.

Generally, as shown in FIG. 1, the servomechanism embodying the present invention includes a sensing unit 10 at the left specifically in the form of a gravity-sensing pendulum, the motion of which is transmited to a central control linkage '12 which is adapted to actuate a control member 14 herein specifically delineated as a valve forming part of a hydraulic control system (not shown). However, it will be clearly understood that the control member 14 can take other forms, for example, a rheostat for an electrical control system.

Additional input to the central control linkage 12 is derived from a reduction gear unit 16 located to the right in FIG. 1 and whose input is in turn received from a manually-controlled shaft 18 or a feedback shaft 20. These shafts 18, 20 may be arranged, by way of example, in the fashion described in US. patent application, Ser. No. 396,827, now Patent No. 3,346,976, for control of the cross-slope of the earth leveling blade of a road grader although other applications will be obvious.

As specifically illustrated, the pendulum 30 is mounted in an oil-filled chamber 32. located to the left of a central partition 34 of a housing. Walls 36 extend from the perimeter of such central partition 34 to the left and receive at their extremities a plate 38 which is bolted in position, as shown, so that the chamber 32-. is substantially enclosed. Adjacent its upper end, the plate 38 is recessed to support a bearing 40 and an aligned bearing 42 is formed in the described central partition 34 to conjointly support a shaft 44 to which the pendulum St) is secured adjacent its upper end by three clamping bolts 46 as shown best in FIG. 1. The chamber 32 is laterally contoured, as shown best in FIG. 3, so as to closely encompass the annular shaft-encompassing portion of the pendulum 30 at its top. Below such uppermost position, the chamber 32 is laterally enlarged so as to accommodate swinging motion of the pendulum whose contour is such that it may swing approximately 15 to the right or to the left from its central disposition. Normally, the housing is mounted on the frame of the equipment to be controlled in a transversely horizontal position so that the pendulum is centered as illustrated in dotted lines in FIG. 2 and in full lines in FIG. 3. From such central position, the pendulum can swing 15 to the left as indicated in phan tom lines in FIG. 3 or approximately the same amount to the right, such extent of swinging being that required to accommodate variances in terrain cross-slope normally encountered by the equipment.

To provide controlled dampening of pendulum motion, the pendulum is closely encompassed transverse to its direction of motion wherefore the flow of oil therearound is restricted. More particularly, as shown clearly in FIG. 1, the sides of the pendulum 30 adjacent-the enclosing plate 38 and the central partition 34 are disposed in close parallelism thereto and as shown best in FIG. 3, the bottom surface of the pendulum is curved about an are centered at its mounting shaft 44 so as to swing closely adjacent a centrally-positioned dampening member 48 which preferably takes the form of a shaft whose central portion within the chamber 32 is flattened as clearly shown at 48a in FIG. 3, wherefore rotation of the shaft will vary the spacing between the bottom of the pendulum 30 and the adjusted dampening member 48. To make such adjustment, the shaft projects through a rotary seal 50 in the lower portion of the described plate 38 and mounts at its exterior extremity a control handle 52 adjacent to which indicia 54 are located to indicate to the operator the degree of dampening, a maximum degree of dampening being indicated when the handle is directed towards the numeral 6 and a minimum being indicated at the position. At the intermediate or 3 position illustrated in FIG. 3, an intermediate amount of dampening is provided when the flat surface 48a of the dampening member 48 is at approximately a 45 disposition. Such dampening control is very effective because of the close spacing between the sides of the pendulum 30 and the adjoining plate 38 and central partition 34 of the pendulum chamber 32 and between the annular upper portion of i the pendulum and the surrounding housing wall as clearly delineated in FIG. 3.

It should be mentioned at this point that any adjustment or maintenance of the pendulum or the associated mechanism is facilitated by the described structure since it is merely necessary to remove the side plate 38 to provide access to the pendulum chamber 32. No other portions of the apparatus need be disturbed by such plate removal.

The described pendulum mounting shaft 44 projects through the bearing 42 in the central partition 34 for operative connection to the mentioned control linkage 12 which is supported within a second chamber 66 encompassed by a cylindrical wall 62 projecting to the right from the central partition 34 and mounting at its extremity the mentioned gear reduction unit 16 which, in effect, closes this second chamber 60 so as to seal the same from the exterior environmental atmosphere. More particularly, a collar 64 is secured to the projecting end of the pendulum shaft 44 within this second chamber 60, such collar 64 being laterally enlarged as best shown in FIGS. 4 and so as to mount a rod 66 in axially parallel relationship to the pendulum shaft but obviously at an eccentric position. Accordingly, if the pendulum shaft 44 rotates, this rod will move in an arcuate path about the pendulum shaft axis. When the pendulum housing is level so that the pendulum 30 is disposed in a central vertical disposition therewithin as shown in full lines in FIG. 3, the rod 66 is disposed in the same horizontal plane as the pendulum shaft 44 as illustrated in FIG. 4. In turn, if the hOUSing for pendulum 30 is tilted so that the pendulum swings to the left as shown in phantom lines in FIG. 3, the rod 66 will 'be moved upwardly and, in turn, if the pendulum 30 swings to the right, the rod will move downwardly from its illustrated posit-ion. Although the rod 66 moves about the axis of the pendulum shaft 44, the relatively short angular motion experienced provides substantially a verticle motion of the rod either upwardly or downwardly from its central illustrated position.

The rod 66 projects forwardly from the end of the pendulum shaft 44 into a bearing 68 at an eccentric location in a generally cylindrical body member 70 which, in turn, rotatably supports by suitable bearings 72, a control ring 74 about its perimeter. A connecting link 76 is pivotally suspended from the lower extremity of this control ring 74 and extends downwardly for pivotal connection at its lower remote end to the upper extremity of an axially-sli-dable valve plunger 78 that is slidable within the valve body 80 of the aforementioned hydraulic control valve 14.

The valve 14 is of conventional construction and in and of itself forms no part of the present invention. Briefly however, upward movement of the plunger 78 places an inlet port 82 in fluid communication with one outlet port 84 whereas movement of the plunger 78 in the opposite direction places the same inlet port 82 in communication with a second outlet port 86, thus ultimately to provide control for double-acting hydraulic cylinders. When centrally disposed, as illustrated, the valve 14 is closed so that flow of hydraulic fluid is precluded.

The cylindrical body member 70 also supports a second ring on its exterior cylindrical surface adjacent to the described control ring 74, the interior of this second ring 90 being depressed at one position for reception of the end of a detent pin 92 projecting from a radial bore in the body member 70 and urged into the depression by a coil spring 94 supported under compression within the bore between the detent pin 92 and a fixed insert 96. Accordingly, this second ring 90 normally rotates with the body member 70 but can, under certain conditions to be explained hereinafter, rotate relative thereto. This ring 90 carries an integral fork 98 at one side and more particularly at the side of the body member 70 remote from the previously described eccentric rod 66. The fork 93 provides a slot 100 within which a control roller 102 is received, such roller being mounted at the extremity of an arm 104 which, as will be described in more detail hereinafter, provides for manual or feedback control of the control linkage 12 and, as a consequence, the valve 14 controlled thereby.

If this roller 102 is in the lateral position illustrated in FIG. 4 and the machine frame is tilted so that the pendulum 30 moves to the left as shown in FIG. 3, the eccentric rod 66 is raised from its central position shown in FIG. 4 to in turn lift the cylindrical body member 70 and the control ring 74 thereon so as to pull the connecting link 76 upwardly and effect a raising of the valve plunger 78 to establish communication through the valve from the inlet port 82 to the first outlet port 84 previously mentioned. The eccentric rod 66, of course, moves arcuately about the axis defined by the pendulum shaft 44 but the entire body member 70 moves upwardly along therewith but about the axis of the described roller 102 which may be considered for present purposes as a fixed pivot. Because of the noted differences in the pivot points of the rod 66 and the body member 70, the roller 102 will shift in its relative disposition within the slot 100. It being observed that the eccentric rod 66 is positioned quite close to the pendulum shaft axis, relatively large swinging of the pendulum 30 effects but a small arcuate motion of the rod to thus provide a desired short stroke of the valve 14 between closed and opened positions. Full swinging of the pendulum 30 does not effect motion of the valve plunger 78 beyond its axial limits. It will also be observed that although the rod 66 moves in an arcuate path, but slight lateral displacement of the connecting link 76 is experienced and substantially axial alignment is preserved between the control linkage 12 and the valve plunger 78. What little misalignment is encountered is of course accommodated by the pivotal connections of the connecting link 76 at its upper and lower extremities.

In turn, if the described roller 102 is moved upwardly or downwardly from its illustrated position within the slot 100, the entire body member 70 will be pivoted about the axis of the previously described eccentric rod 66 to effect a raising or lowering of the connecting link 76 and the valve plunger 78 connected thereto. If excessive motion of roller 102 is experienced, the valve plunger 78 may reach its axial limit in one direction or the other. Valve damage is avoided by withdrawal of the detent pin 92 from its resilient connection to the ring 90 so that no further valve movement occurs.

The position of the roller 102 is determined alternatively by the mentioned manual control shaft 18 or the feedback shaft 20 which constitute dual inputs to the gear reduction unit 16 whose output shaft 106 carries the roller arm 104. Preferably, as shown in FIG. 6, the manual control shaft 18 projects into the gear reduction unit 16 at the upper right thereof, being centrally supported by suitable bearings 110 and carrying at its inner extremity a small gear 112 which meshes with the exterior of an internal-external ring gear 114 having a lateral flange enabling support of the ring gear for free rotation on suitable exterior bearings 116 within the gear housing 118. In turn, the interior teeth of the internal-external ring gear 114 mesh with a planetary 120 whose mounting shaft 122 is secured to a planetary carrier 124 centrally keyed to an intermediate transmission shaft 126 Interiorly, the planetary 120 also meshes with the exterior of a sun gear 128 secured to the previously mentioned feedback shaft 20 that is preferably suported by suitable bearings 130 in axial alignment with the intermediate shaft 126.

If it is assumed that the feedback shaft 20 is not revolving, any rotation of the manual control shaft 18 will, of course, effect rotation of the small gear 112 at its end. Resultant rotation of the meshing internal-external ring gear 114 is in turn transmitted to the planetary 120 which is thus forced to move about the sun gear 128 stationary with the feedback shaft 20 so as to effect rotation of the planetary carrier 124 and the intermediate shaft 126 to which it is secured. On the other hand, if the manual control shaft 18 is stationary and the feedback shaft 20 is rotated, the sun gear 128 at the inner end of the feedback shaft 20 will rotate therewith to effect rotation of the planetary 120. Because of its engagement with the internal-external ring gear 114 which is now fixed by its connection to the manual control shaft 18, the planetary 120 rotates to effect a final motion of the planetary carrier 124 and the intermediate shaft 126 to which it is mounted. If both the feedback and manual control shafts 20, 18 are rotating at the same time, a summation of their rotation is delivered to the intermediate shaft. Thus a relatively simple dual input to the intermediate shaft 126 is provided.

The described intermediate shaft 126, located in the central portion of the gear housing 118 in axial alignment with the described feedback shaft 20, is mounted in suitable bearings 132 within the housing and carries two sun gears 134, 136 at axially-spaced positions, the one sun gear 134 having a slightly lesser diameter than the other. The first and smaller sun gear 134 meshes with a planetary gear 137 carried by a planetary carrier 138 and also meshing with an internal ring gear 140 fixedly mounted on the interior of the gear housing 118 in concentric relationship with the sun gear 134 and the intermediate shaft 126. In turn, the second, larger sun gear 136 is in mesh with a planetary gear 142 which is smaller than planetary gear 137 and is secured to the same planetary carrier 138. This second planetary gear 142 engages externally an internal ring gear 144 of a diameter equal to the fixed ring gear 140. However, ring gear 144 is mounted for rotation in suitable bearings 146 and forms an integral part of a plate which extends inwardly beyond the end of the intermediate shaft 126 for connection to the output shaft 106 which also can be integral therewith and projects from the left end of the housing 118 to mount the aforementioned roller arm 104 on its extremity. Preferably, a spiral spring 148 is connected between the shaft 106 and the housing 118 to eliminate any ring gear lash.

Rotation of the intermediate shaft 126 will be transmitted through the described planetary system to the output shaft 106 with a reduction ratio determined by the relative diameters of the two sun gears 134, 136. More particularly, as the intermediate shaft 126 rotates, both sun gears 134, 136 will rotate therewith to instigate rotation of the planetary gears 137, 142. Since the diameters of the sun gears are different and yet both planetary gears are carried by the same planetary carrier 138, a tendency for different motion of the planetary carrier will exist. Since the one planetary 137 is in engagement with the fixed internal ring gear 140 which provides a reactive element, a differential motion of the planetary carrier 138 will be experienced to effect a predetermined motion of the second planetary 142 which is in engagement with the rotatable ring gear 144 whose resultant motion is then transferred to the output shaft 106. A very high step-down gear ratio can be obtained between the intermediate shaft 126 and the output shaft 106; as shown, such ratio is approximately 200 to 1. Additionally, it may be noted that the illustrated dual input gearing necessitates more revolutions of the manual control shaft 18 than that of the feedback shaft 20 to provide for the same rotation of the intermediate shaft 126. The disclosed arrangement provides a 4 to 1 ratio beween the manual and feedback shafts and the overall gear reduction ratio between the manual control shaft 18 and the output shaft 106 is 800 to 1 while the corresponding overall ratio beween the feedback shaft 20 and the output shaft 106 is 200 to 1. Preferably, one revolution of the manual shaft 18 is equivalent to a change of one percent in the cross-slope of the working implement being controlled by the described apparatus. It will then be obvious that one revolution of the feedback shaft 20 results from an angular variation of the crossslope of the working implement of four percent.

The mentioned arm 104 extends radially from the output shaft 106 and carries at its outer extremity a pin 150 which projects therefrom in parallelism to the output shaft and this pin, in turn, carries at its outer extremity the aforementioned roller 102 which projects into the slot 100 on the feedback control ring of the control linkage 12. More particularly, the roller 102 is tapered inwardly where it enters the slot and a corresponding taper is formed on the interior surfaces of the slot. The roller 102 is carried both for rotation and for axial sliding movement on the pin and is urged into contact with the slot surfaces by a coil spring 152 compressed between the roller 102 and the radial arm 104. Accordingly, if the roller 102 becomes worn, it is still urged into contact with the slot surfaces and thus maintains accurate controlling engagement therewith.

As previously mentioned, the described gear reduction unit 16 is mounted at the extremity of the wall 62 encompassing the second chamber 60. More particularly, an exterior mounting flange on the gear housing 118 is bolted to the wall 62 of the chamber by suitable bolts 162 which also pass through enlarged bolt holes 164 in the mounting flange 160 and arcuate slots 166 in an annular ring 168 having an inner flange 168a which projects interiorly of the mounting wall 62. This flange 168a varies in thickness to provide an eccentric support for the gear reduction unit 16 wherefore rotation of the mounting ring 168 prior to application of the mounting bolts 162 will slightly change the disposition of the gear reduction unit 16 and, as a consequence, the position of the actuating roller 102 relative to the control linkage 12. Such variable eccentric mounting of the gear reduction unit 16 accordingly provides for slight variation in the leverage ratio delivered to the control linkage 12 by the roller 102. Thus, a simple mechanism for adjusting motion of the valve 14 relative to motion of the controlled working implement is provided.

Under certain operational conditions as shown, for example, in the mentioned US. patent application, Ser. No. 396,827, the described unit is mounted on the main frame of the road grading equipment so that the pendulum mounting shaft 44 is longitudinally aligned therewith and so that the pendulum 30 lies in its central disposition when the machine frame is transversely horizontal. The manual control shaft 18 is connected by suitable linkage to a control handle adjacent the operators seat and the feedback control shaft 20 is in turn connected through suitable linkage to the working implement (earth leveling blade) so as to sense changes in its transverse slope relative to the main frame of the machine from which it is adjustably mounted by suitable double-acting hydraulic cylinders that are in fluid communication with the described control valve 14.

If the machine frame is transversely horizontal and it is desired to grade a surface with a three percent crossslope, the manual control shaft 18 is rotated to change the position of the roller 1G2 and through the described control linkage 12 to effect a raising or lowering of the valve plunger 78, thus to actuate the hydraulic cylinder or cylinders to adjust the transverse disposition of the blade until the desired three percent cross-slope is attained. As the disposition of the blade varies, rotation of the feedback shaft 20 is effected to, in turn, change the roller disposition in a direction opposite to that formerly effected by the rotation of the manual control shaft 18, such action continuing until the roller 102 has regained its initial position Whereat the valve 14 is again closed and no further adjustment of the blade cross-slope is made.

If motion of the machine is now instigated, it will move onto the three percent slope wherefore one side of the machine Will be raised so as to tilt the pendulum housing and effect a relative swinging of the pendulum 30 so that the latter remains in its vertical disposition within the first chamber 32. Such swinging of the pendulum is, of course, transmitted through its shaft 44 to the control linkage 12 and ultimately to the valve 14 to effect a raising or lowering of the valve plunger 78 wherefore hydraulic fluid is delivered to the hydraulic cylinders so as to effect a tilting of the blade in a direction opposite to the encountered tilting of the main frame and thus reestablish the precise three percent transverse slope of the blade. As the blade disposition varies, such variance is delivered through the feedback shaft 20 and the gear reduction unit 16 to vary the disposition of the roller 102 which effects operation of the control linkage 12 in a direction opposite to that formerly effected by the swinging of the pendulum 30 and the valve plunger 78 is gradually returned to its central closed position whereupon no further tilting of the blade relative to the machine frame is experienced.

If any correction errors are experienced, a simple adjustment of the pendulum 30 on its mounting shaft or rotation of the eccentric ring 168 mounting the gear reduction unit 16 enables a quick effective establishment of the proper control proportions.

It extremely uneven terrain is encountered by the entire machine, the dampening control handle 5'2 is adjusted to a higher setting so that any instantaneous shocks delivered to the frame and thus to the pendulum 30 do not effect repetitive actuations of the valve 14. Thus, the noise level of the apparatus is reduced. On the other hand, if a fine grading operation is to be achieved over relatively smooth terrain, the dampening control handle 52 is rotated to a minimum setting so that the pendulum actuation becomes more sensitive and the ultimate in grading accuracies can be achieved. In practice, it has been found that fine grading of a ten foot strip can be achieved automatically with transverse grading deviations of less than A; inch across the entire span.

As described operationally, the servomechanism housing is mounted on the machine frame and the described feedback connection is utilized. Alternatively, the unit can, if desired, be mounted directly on the working implement and no feedback connection is necessary. In such case, the feedback shaft 20 Will merely be fixed in place.

Many further modifications can be envisioned without departing from the spirit of the present invention and the foregoing description of one embodiment is accordingly to be considered purely as exemplary and not in a limiting sense. The actual scope of the invention is to be indicated only by reference to the appended claims.

What is claimed is:

1. A servomechanism for automatically controlling the disposition of the working implement of earth leveling equipment or the like which comprises means including a rectilinearly movable control member adapted for operative connection to the working implement to adjust the disposition thereof,

a sensing unit having an output shaft whose rotary position changes in response to a variation in the sensed information, and

control linkage connecting said shaft to said control member, said control linkage including a cylindrical body member,

a first control ring mounted for rotation on said body member,

a connecting link pivotally joined at its opposite extremities to said first control ring and said control member,

a second ring on said body member,

means forming a pivot for said second ring laterally relative to said connecting link, and

an eccentric rod on said output shaft and operatively connected to said body member at a position laterally of said connecting link on the remote side thereof relative to said pivot.

2. A servomechanism according to claim 1 which comprises means mounting said pivot for movement in a direction substantially parallel to the disposition of said connecting link.

3. A servomechanism according to claim 2 wherein said pivot moving means includes a rotary shaft,

a radial arm secured to said shaft, and

a roller mounted at the outer extremity of said radial arm to form said pivot.

4. A servomechanism according to claim 3 which comprises means mounting said roller-supporting shaft for adjustment about a predetermined axis.

5. A servomechanism according to claim 3 which comprises means forming a radially extending slot on said second ring for engagement with said roller.

6. A servomechanism according to claim 5 wherein said slot and said roller include tapered engaging surfaces and said roller is resiliently urged into said slot.

7. A servomechanism for automatically controlling the disposition of the working implement of earth leveling equipment or the like which comprises means including a rectilinearly movable control member adapted for operative connection to the working implement to adjust the disposition thereof,

a sensing unit having an output shaft whose rotary position changes in response to a variation in the sensed information, and

control linkage connecting said shaft to said control member, said control linkage including means forming an adjustable pivot,

a body member connected to said control member and mounted for motion about said pivot and an eccentric member on said shaft and operatively connected to said body member to effect motion of said body member about said pivot in response to rotation of said shaft.

8. A servomechanism for automatically controlling the disposition of the working implement of earth leveling equipment or the like which comprises means including a control member adapted for operative connection to the working implement to adjust the disposition thereof,

a sensing unit having an output shaft whose rotary position changes in response to a variation in the sensed information,

control linkage connecting said shaft to said control member, and

means including a second shaft operatively connected to said control linkage to adjust said control member, and

means for controlling the rotary disposition of said second control shaft including a reduction transmission having an output ring gear connected to said shaft,

a planetary gear engaging said output ring gear,

a second planetary gear of different diameter than said first planetary gear,

a common planetary carrier for said first and second planetary gears.

21 pair of spaced sun gears of different diameters operatively connected to said planetary gears,

a single shaft mounting both of said sun gears for rotation therewith,

a fixed ring gear engaging said second planetary gear,

and

means for adjusting the rotative position of said sun gear mounting shaft including a rotary feedback shaft operatively connected between said sun gear mounting shaft and the Working implement.

References Cited UNITED STATES PATENTS 487,994 12/ 1892 Clifi 74-705 1,301,948 4/1919 Kaplan et al. 74-89 X 1,786,158 12/1930 Hawes 74-705 2,302,358 11/1942 Von Tavel 91-382 2,431,659 11/1947 Flounders 251-54 2,586,941 2/1952 Gretener et al. 74-388 2,934,078 4/1960 Gurries et al. 137-45 2,961,783 11/1960 Bowen et al. 37-156 3,146,585 9/1964 Gulick 74-89 X 3,164,915 1/1965 Benner et al. 37-156 30 DONLEY I. STOCKING, Primary Examiner.

THOMAS C. PERRY, ROBERT A. OLEARY,

Exmnim'rs. 

